GATE 2013 · session-1
Three concurrent processes X,Y,Z execute three different code segments that access and update certain shared variables. Process X executes the P operation (i.e., wait) on semaphores a,b,c; process Y executes the P operation on semaphores b,c,d; process Z executes the P operation on semaphores c,d,a before entering the respective code segments. After completing its code segment, each process invokes the V operation (i.e., signal) on its three semaphores. All semaphores are binary semaphores initialized to one. Which one of the following represents a deadlock-free order of invoking the P operations by the processes?